As mobile devices have been increasingly developed and the demand for such mobile devices has increased, the demand for secondary batteries has sharply increased as an energy source for the mobile devices. Among such secondary batteries is a lithium secondary battery having high energy density and discharge voltage, into which much research has been carried out and which is now commercialized and widely used.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-type secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, meanwhile, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, which exhibit high energy density, discharge voltage, and output stability, is very high.
Based on the shape thereof, secondary batteries may be classified into a cylindrical battery cell, a prismatic battery cell, and a pouch-type battery cell. Among these kinds of secondary batteries, much interest is currently focused on the pouch-type battery cell, which can be stacked with high integration, has high energy density per unit weight, can be manufactured at low cost, and can be easily modified.
FIG. 1 is an exploded perspective view typically showing a general structure of a conventional representative pouch-type secondary battery.
Referring to FIG. 1, a pouch-type secondary battery 100 includes a stacked type electrode assembly 30 having pluralities of electrode tabs 31 and 32 protruding therefrom, two electrode leads 40 and 41 respectively connected to the electrode tabs 31 and 32, and a battery case 40, in which the stacked type electrode assembly 30 is received in a sealed state such that the electrode leads 40 and 41 are partially exposed outward from the battery case 20.
The battery case 20 includes a lower case 21 having a concave receiving part 23, in which the stacked type electrode assembly is located, and an upper case 22 for covering the lower case 21 such that the stacked type electrode assembly 30 is received in the battery case 20 in a sealed state. The upper case 22 and the lower case 21 are connected to each other by thermal welding in the state in which the stacked type electrode assembly 30 is mounted therein to form a sealed part 24.
FIG. 1 shows a pouch-type battery cell configured to have a structure in which electrode terminals, constituted by the electrode tabs and the electrode leads connected to the electrode tabs, are formed at one end of the electrode assembly. Alternatively, a pouch-type battery cell configured to have a structure in which electrode terminals are formed at one end and the other end of an electrode assembly may be included in the scope of the present invention as an embodiment of the present invention.
In addition, FIG. 1 shows a pouch-type battery cell using a stacked type electrode assembly. Alternatively, a pouch-type battery cell using a wound type or jelly-roll type electrode assembly may be configured to have the above-described structure.
As shown in FIG. 1, the pouch-type battery cell is generally configured to have an approximately rectangular hexahedral shape. However, the size and thickness of electronic devices have been continually reduced so as to satisfy the desires of consumers. In order to maximize space utilization, therefore, it is necessary to provide various shapes of batteries corresponding to the shapes of the devices and, in addition, to efficiently utilize the internal space in each of the devices.
Particularly, in recent years, the design of the devices has played a very important role when consumers choose the devices. For this reason, various designs are provided in place of a flat type design based on high productivity. For example, electronic devices, such as mobile phones and laptop computers, may be designed such that the devices can be curved in an ergonomic manner. For example, the sides of a smart phone may be curved so as to be easier to grip, and a flexible display device may be curved or bent. That is, the flexible display device may be manufactured to have various shapes.
In the case in which a battery cell or battery pack configured to have a rectangular hexahedral shape is mounted in a device designed so as to have such curved parts or a device that can be curved, however, the efficiency of utilization of the space in the device may be lowered. In recent years, therefore, it has been required for the battery cell to be flexible such that the battery cell can be easily mounted in devices configured to have various kinds of designs.
Therefore, there is a high necessity for technology that is capable of solving problems that may occur when the battery cell is bent while solving the above problems.